Anorexia Nervosa (AN) is a debilitating psychiatric illness with physical and psychological sequelae. AN, which is characterized by significant malnourishment, often emerges in adolescence, a period of rapid brain development and maturation. Effectively intervening at this pivotal period may circumvent potentially irreversible damage and restore adolescents to a more normal developmental trajectory. Recent progress in treating adolescents with AN supports the importance of family involvement. However, the most optimal manner to incorporate the family requires further study, particularly given the significant caregiver burden and frequent psychopathology reported among AN family members. Preliminary evidence indicates that separated family treatment (SFT), in which a family intervention is delivered to adolescent and caregiver separately, may be more appropriate than conjoint interventions for families with difficulties such as high expressed emotion. Family-based treatments that target trait features associated with AN, such as behavioral and cognitive rigidity, high harm avoidance, and poor interoceptive awareness may prevent symptom relapse as these young people encounter new life stressors. The purpose of the proposed research is to develop a treatment for adolescent AN that includes the family in a way that has broad appeal and applicability (even with more distressed families) and incorporates newer technologies from behavior therapy which may be well-suited to address trait features of AN. These newer technologies are acceptance-based and specifically designed to target behavioral rigidity in the presence of difficult thoughts, feelings, and bodily sensations. The specific aims of this treatment development project are as follows: 1) develop and refine a 20 session, 24 week acceptance-based separated family treatment for adolescents with anorexia nervosa (ASFT) that combines an existing state-of-the- art parent therapy component (Zucker, 2008) with an innovative individual adolescent component, 2) evaluate the acceptability and feasibility of the treatment program, and 3) provide preliminary data regarding the efficacy of the treatment approach. Treatment development will be iterative, and will occur over three phases. Each phase will implement an increasingly refined version of the treatment, evaluate credibility and expectancy of treatment, adherence, and obtain qualitative and quantitative feedback from participants. Multimodal assessment will be employed;and participants will be assessed at baseline, 10 weeks, post-treatment, and three months post-treatment. It is anticipated that the resultant data and treatment manual will set the stage for a large scale RCT comparing ASFT to more traditional family treatments. PUBLIC HEALTH RELEVANCE: Anorexia nervosa (AN) is a debilitating mental illness with the potential to permanently dislodge adolescents from healthy developmental trajectories. Involvement of the family is essential for effective management, however, the degree of caregiver burden is extreme. Interventions that involve the family and yet target acute symptom management, ease caregiver burden, and address trait features associated with illness relapse are essential for sustained recovery from these threatening disorders.